Here's a simple way to calculate your
GPH at any RPM. It came from a great article about how to
calculate your GPH (gallons per hour). It's by Mike Carson and appeared in
the April 1981 issue of Motor Boat and Sailing. But, I have condensed it down to
the "meat" for those of you who just want to "get it done"!
There is a link on that page to the full article if you want to get it in its
entirety.

I did a rough calculation of Knot Kidding, click here
to see the graph.. Actually, in practice, we average 4.5 - 5 GPH, including some
generator use. Not bad!!!